Maspin/SerpinB5 is a cytoskeleton-binding protein that regulates epithelial cell shape

Maspin/SerpinB5 is an abundant and pleiotropic protein mostly expressed by epithelia. Initially described as a tumor suppressor, it has been reported as a regulator of cell adhesion, migration, and invasion. How intracellular Maspin orchestrates these processes is poorly understood. In this study, we utilized Affinity purification-Mass spectrometry (AP/MS) alongside in vitro reconstitution assays to establish that Maspin directly interacts with microtubules and microfilaments. Additionally, CRISPR/Cas9-mediated GFP tagging of endogenous Maspin, combined with immunostaining, revealed its localization at the cortical cytoskeleton and the mitotic spindle. Depletion of Maspin by RNAi and CRISPR/Cas9 in non-transformed epithelial cell lines modifies cell-cell contact and promotes cytoskeletal rearrangements. Concomitantly, we observed a modest upregulation of mesenchymal markers during interphase and abnormal cell rounding during mitosis. An evaluation of Maspin's effect on microtubules revealed that it suppresses their growth in vitro and in cells. Collectively, these results demonstrate that Maspin acts dynamically at the interface of the cytoskeleton and adhesion sites, modulating cell shape. The non-inhibitory serpin Maspin (SerpinB5) directly binds to microfilaments and microtubules in vitro and in cells, acting at the interface between the cytoskeleton and adhesion sites.